This application is based on application No. 2000-215098 filed in Japan, the content of which is hereby incorporated by reference.
(1) Field of the Invention
The present invention relates to a radio information terminal (hereinafter xe2x80x9cmobile stationxe2x80x9d) that connects to abase station, for example a telephone and a portable information communication device, and a radio communication system made up of the radio base station and the mobile station. In particular, the present invention relates to improved efficiency of frequency usage in the system.
(2) Description of the Related Art
Recently with the number of mobile stations, including portable telephones and portable communication devices, on the rise there is increasing demand in society for more effective use of frequency resources. Path division multiple access and the wireless zone system (the latter is also called the cellular system) are techniques which respond to this demand.
Path division multiple access is a system in which a radio base station uses a directional antenna to communicate with a plurality of mobile stations at the same time but in different directions using the same carrier wave frequency.
An example of a directional antenna that is used in the radio base station in path division multiple access is an adaptive array apparatus. The adaptive array apparatus is composed of a plurality of antenna devices which are provided fixed. The adaptive array apparatus forms a directivity pattern (also called xe2x80x9carray antenna patternxe2x80x9d) for reception and transmission for the antenna as a whole by movably varying the amplitude and phase of the reception and transmission signals for each antenna device.
The adaptive array apparatus, in forming the directivity pattern, not only increases transmission strength and reception sensitivity towards a desired mobile station, but also reduces transmission strength and reception sensitivity toward other mobile stations. Note that details of an adaptive array apparatus are contained in xe2x80x9cAdaptive Signal Processing in Space Areas and its Applied Technology Special Featurexe2x80x9d (Journal of the Institute of Electronics, Information and Communication Engineers Vol. J75-B-2 No. 11).
The wireless zone system is a system in which a service area is divided into sectors called zones and a frequency to be used for a carrier wave is allocated to each zone. Each radio base station and mobile station in the zone communicates using the allocated frequency of a carrier wave, and the same frequency is allocated repeatedly to zones which are in positions in which interference does not occur.
FIG. 10 is a schematic drawing for explaining path division multiple access and the wireless zones. 900 shows a service area, 901 shows one wireless zone, 902 shows the frequency allocated to the wireless zone, 903 shows a radio base station, 904 and 905 show mobile stations, 906 and 907 show radio base station directivity patterns in relation to the mobile stations 904 and 905 respectively, and 908 and 909 show the respective directivity patterns of the mobile stations 904 and 905.
Here the directivity patterns show, for communication within one wireless zone, a range in which transmission signals from the radio base station and the mobile station reach their destination with adequate strength, and a range in which the radio base station and the mobile station can receive signals with adequate sensitivity. These ranges are also understood to be ranges in which interference with communication in other wireless zones which use the same frequency occurs.
In the drawing the radio base station 903 communicates with the mobile stations 904 and 905 according to path division multiplexing using a carrier wave frequency f1 by forming different directivity patterns 906 and 907. The drawing shows schematically that the frequency f1 is allocated again to a wireless zone outside of the directivity patterns of the radio base station 903 and the mobile stations 904 and 905. Note that conventionally the mobile stations 904 and 905 transmit and receive signals with a uniform directionality in all directions.
In the path division multiple access system, the radio base station changes its directivity patterns following the movements of each mobile station using the adapter array apparatus, in order to avoid mixing of voices and to maintain communication quality. Control substance of the directivity pattern during reception and transmission according to minimum mean square error (MMSE) when there are N antenna devices is shown below.
The control of the directivity pattern during reception is for controlling extraction of a reception signal from a specific mobile station by suitably compositing signals received through each antenna device.
FIG. 11 is an outline showing control contents according to MMSE when a signal from the mobile station is received by the adaptive array apparatus.
y(t)=w(txe2x88x921)*x(t)=w1(txe2x88x921)*x1(t)+w2(t1)*x2(t)+ . . . +wN(txe2x88x921)*xN(t)xe2x80x83xe2x80x83 less than Equation 1 greater than 
This control, as shown in the figure and in Equation 1, is performed to obtain a total sum y(t) by multiplying the reception signal vectors x1(t), x2(t), . . . , xN(t) which are constituted from each signal actually obtained through the antenna devices, with the weight vectors w1(txe2x88x921), w2(txe2x88x921), . . . , wN(txe2x88x921) which are constituted from each weight coefficient corresponding to each antenna. This control is for determining appropriate weight vectors so that y(t) includes a maximum of components of the reception signal from the mobile station from which the signal is being extracted, and so that y(t) includes a minimum of components of reception signals from other mobile stations.
Here, t shows the time that the signal reaches the radio base station and is, for example, a value showing an elapsed time within a timeslot in the PHS Standard and is used as a unit of time taken to receive 1 symbol. Therefore, the reception signal vector x, the weight vector w and so on are a signal series corresponding to values 1, 2, . . . . Furthermore, the weight vector w is a parameter for forming the directivity pattern, and the weight vector w and the reception signal vector x express as a complex vector a signal which has amplitude and phase.
The initial value of the weight vector is set appropriately, and the weight vector is updated each unit of time by being varied within a predetermined range in a manner explained below, so that the difference between a particular part of the signal (hereinafter xe2x80x9creference signalxe2x80x9d) sent from the mobile station d(t) and the signal y(t) is a minimum. The particular part is a part of the signal which is predetermined and fixed, for example, a preamble and a UW (unique word) which are symbol synchronization codes in the PHS Standard.
e(t)=d(t)xe2x88x92y(t)=d(t)xe2x88x92xcexa3(wi(txe2x88x921)*xi(t))xe2x80x83xe2x80x83 less than Equation 2 greater than 
As shown in Equation 2, in each time t the difference e(t) between the signal y(t) calculated using the weight vector in time txe2x88x921 and the reference signal d(t). Wi(t) is calculated by correcting wi(txe2x88x921) so that the difference is a minimum. Theoretically, by repeating this calculation each time, the value of the weight vector converges at a constant value, and the signal y(t) becomes close to the signal of the mobile station from which the signal is being extracted.
The preamble and the unique word that are represented by the reference signal are sent before target data, which is the content of the communication, therefore the signal y(t) shows substantially the signal of the mobile station that is being extracted at the point of reception of the target data. Note that after conversation starts, the last weight vector value obtained in the previous time slot, for example, is used as the initial value in the following time slot.
Control of the directivity pattern in reception is a process of distributing a specific transmission signal in correspondence to each antenna device, multiplying a final weight vector corresponding to each antenna device obtained at reception with each distributed signal, and transmitting the obtained signals simultaneously from the antenna devices. According to this process, a transmission gain which is directional to the specific mobile station can be obtained, and the strength of transmission signals in directions of other mobile stations can be suppressed.
In this way, the radio base station extracts the signal from the specific mobile station, while adjusting the weight vector based on the signals received through the plurality of antennas and the information about the section of the preamble and the unique word whose signal content is already known. By using the weight vector to direct the directionality towards the specific mobile station during reception, communication is performed with each mobile station using path division multiple access avoiding interference to an extent and maintaining quality.
As explained above, in conventional radio communication systems, a plurality of mobile terminals are connected using one frequency carrier wave according to path division multiple access based on directional control in a radio base station. Furthermore, the same frequency can be reused by putting a set distance therebetween according to the wireless zone system. This allows for more effective usage of frequency resources.
However, a dramatic increase in the number of users of radio communication systems has put further pressure on frequency resources, even when the path division multiple access and wire less zone methods are used, leading to a demand to further increase the number of mobile stations that can be connected, while using fixed frequency resources.
The object of the present invention is to provide a radio communication system and a mobile station for the system that increase the number of mobile stations that can be connected using fixed frequency resources, while maintaining communication quality.
In order to achieve the stated objective, (1) a radio information terminal of the present invention is a radio information terminal which communicates with a radio base station, including a calculation unit for calculating data for controlling antenna directivity; and a reception unit for forming, using the calculated data, an antenna directivity in which reception gain of a signal transmitted from the radio base station increases, and receiving the signal using the formed directivity.
According to the stated construction, interference signals from other radio base stations can be eliminated because the radio information terminal forms reception directivity in the direction of the radio base station with which it is to communicate. The radio base station conventionally has the ability to eliminate signals being received from other radio information terminals and not to output interference signals to other radio in formation terminals. This is because the radio base station transmits and receives by performing directivity control in the direction of the radio information terminal with which it is to communicate. By working in cooperation the radio information terminal and the radio base station can shorten the distance between re-usage of frequency and improve frequency usage efficiency.
(2) The radio information terminal of (1) may further include an obtaining unit for obtaining a code for synchronization with symbols, the symbols being part of the signal, and the code being notified from the radio base station; and a storage unit for storing the obtained code, wherein the calculation unit calculates, based on the stored code, the data for controlling antenna directivity for each symbol.
According to the stated construction, the radio information terminal forms directivity based on the symbol synchronization code which is notified from the radio base station. By the radio base station which notifies each radio information terminal of a different symbol synchronization code and the radio information terminal working in cooperation, the radio information terminal reduces errors in synchronizing with signals for other terminals, can form directivity patterns accurately, and improves communication quality.
(3) In the radio information terminal of (2) the code may show one of (a) a preamble part of the signal, (b) a unique word part of the signal, and (c) the preamble part of the signal and the unique word part of the signal.
According to the stated construction the same effect as (2) is obtained.
(4) The radio information terminal of (2) may further include a generation unit for generating, by modulating the stored code, a reference signal which is a basis for forming the antenna directivity, wherein the data for controlling the antenna directivity is expressed as a weight coefficient in relation to each antenna signal, the calculation unit calculates a weight coefficient so that a difference between (a) a signal obtained by multiplying the signal received by each antenna with the weight coefficient and adding each resultant signal together, and (b) the reference signal decreases, and the reception unit forms the directivity by multiplying the signal received by each antenna with the weight coefficient and adding each resultant signal together.
According to the stated construction the same effect as (2) is obtained.
(5) The code in the radio information terminal of (4) may show one of (a) a preamble part of the signal, (b) a unique word part of the signal, and (c) the preamble part of the signal and the unique word part of the signal.
According to the stated construction the same effect as (4) is obtained.
(6) The radio information terminal of (4) may further include a transmission unit for forming antenna directivity so that transmission gain of a signal being transmitted towards the radio base station increases, by multiplying a transmission signal for each antenna with the weight coefficient and issuing a resultant signal.
According to the stated construction the radio information terminal can further shorten the space between reusage of frequencies and improve frequency usage efficiency, because it reduces the interference signal power radiated to radio base stations other than the one with which it is to communicate.
(7) The code in the radio information terminal of (6) may show one of (a) a preamble part of the signal, (b) a unique word part of the signal, and (c) the preamble part of the signal and the unique word part of the signal.
According to the stated construction the same effect as (6) is obtained.
(8) A radio communication system of the present invention includes a radio base station for allocating a different code to each radio information terminal, notifying each radio information terminal of the allocated code, incorporating the allocated code in information for the radio terminal, and transmitting the information to the radio terminal; and the radio information terminal of Claim 1.
According to the stated construction the same effect as (1) is obtained.
(9) A radio communication system of the present invention a radio base station for allocating a different code to each radio information terminal, notifying each radio information terminal of the allocated code, incorporating the allocated code in information for the radio terminal, and transmitting the information to the radio terminal; and the radio information terminal of Claim 2.
According to the stated construction the same effect as (2) is obtained.
(10) A radio communication system of the present invention a radio base station for allocating a different code to each radio information terminal, notifying each radio information terminal of the allocated code, incorporating the allocated code in information for the radio terminal, and transmitting the information to the radio terminal; and the radio information terminal of Claim 3.
According the stated construction the same effect as (3) is obtained.
(11) A radio communication system of the present invention a radio base station for allocating a different code to each radio information terminal, notifying each radio information terminal of the allocated code, incorporating the allocated code in information for the radio terminal, and transmitting the information to the radio terminal; and the radio information terminal of Claim 4.
According to the stated construction the same effect as (4) is obtained.
(12) A radio communication system of the present invention a radio base station for allocating a different code to each radio information terminal, notifying each radio information terminal of the allocated code, incorporating the allocated code in information for the radio terminal, and transmitting the information to the radio terminal; and the radio information terminal of Claim 5.
According to the stated construction the same effect as (5) is obtained.
(13) A radio communication system of the present invention a radio base station for allocating a different code to each radio information terminal, notifying each radio information terminal of the allocated code, incorporating the allocated code in information for the radio terminal, and transmitting the information to the radio terminal; and the radio information terminal of Claim 6.
According to the stated construction the same effect as (6) is obtained.
(14) The radio communication system of the present invention a radio base station for allocating a different code to each radio information terminal, notifying each radio information terminal of the allocated code, incorporating the allocated code in information for the radio terminal, and transmitting the information to the radio terminal; and the radio information terminal of Claim 7.
According to the stated construction the same effect as (7) is obtained.
(15) A radio communication method of the present invention is a communication method used by a radio information terminal which communicates with a radio base station, including a calculation step for calculating data for controlling antenna directivity; and a reception step for forming, using the calculated data, an antenna directivity in which reception gain of a signal transmitted from the radio base station increases, and receiving the signal using the formed directivity.
According to the stated construction the same effect as (1) is obtained.
(16) The communication method of (15) may further include an obtaining step for obtaining a code for synchronization with symbols, the symbols being part of the signal, and the code being notified from the radio base station; and a storage step for storing the obtained code, wherein the calculation step calculates, based on the stored code, the data for controlling antenna directivity for each symbol.
According to the stated construction the same effect as (2) is obtained.
(17) The communication method of (16) may further include a generation step for generating, by modulating the stored code, a reference signal which is a basis for forming the antenna directivity, wherein the data for controlling the antenna directivity is expressed as a weight coefficient in relation to each antenna signal, the calculation step calculates a weight coefficient so that a difference between (a) a signal obtained by multiplying the signal received by each antenna with the weight coefficient and adding each resultant signal together, and (b) the reference signal decreases, and the reception step forms the directivity by multiplying the signal received by each antenna with the weight coefficient and adding each resultant signal together.
According to the stated construction the same effect as (2) is obtained.
(18) The communication method of (17) may further include a transmission step for forming antenna directivity so that transmission gain of a signal being transmitted towards the radio base station increases, by multiplying a transmission signal for each antenna with the weight coefficient and issuing a resultant signal.
According to the stated construction the same effect as (6) is obtained.
(19) A program of the present invention is a computer executable program for realizing a communication method used by a radio information terminal which communicates with a radio base station, executing on a computer: a calculation step for calculating data for controlling antenna directivity; and a reception step for forming, using the calculated data, an antenna directivity in which reception gain of a signal transmitted from the radio base station increases, and receiving the signal using the formed directivity.
According to the stated construction the same effect as (1) is obtained.
(20) The program of (19) may further execute an obtaining step for obtaining a code for synchronization with symbols, the symbols being part of the signal, and the code being notified from the radio base station; and a storage step for storing the obtained code, wherein the calculation step calculates, based on the stored code, the data for controlling antenna directivity for each symbol.
According to the stated construction the same effect as (2) is obtained.
(21) The program of (20) may further execute a generation step for generating, by modulating the stored code, a reference signal which is a basis for forming the antenna directivity, wherein the data for controlling the antenna directivity is expressed as a weight coefficient in relation to each antenna signal, the calculation step calculates a weight coefficient so that a difference between (a) a signal obtained by multiplying the signal received by each antenna with the weight coefficient and adding each resultant signal together, and (b) the reference signal decreases, and the reception step forms the directivity by multiplying the signal received by each antenna with the weight coefficient and adding each resultant signal together.
According to the stated construction the same effect as (2) is obtained.
(22) The program of (21) may further execute a transmission step for forming.
directivity so that transmission gain of a signal being transmitted towards the radio base station increases, by multiplying a transmission signal for each antenna with the weight coefficient and issuing a resultant signal.
According to the stated construction the same effect as (6) is obtained.